Are the signals in this scenario clear?

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There’s famine in the region, and a convoy of merchants arrives in the character’s walled town while pursued by undead monsters created by this famine. The players are effectively informed of the famine, and the de-facto leader of the town’s defenses tells them that the priority would be to set up a trade route with another town, which is apparently doing better. Before departing, the merchants of the convoy explain that, on the road to get to the PC’s town, they were attacked multiple times: first by goblins, then by bandits, and finally by the undead. They also say that more than a third of the convoy was wiped out between the goblins and the bandits. They then mark the positions of the attacks on the party’s map. The party departs and decides to follow the same route of the merchants, despite being slower (no horses) and less in number (the merchants were dozens of people).

The PCs get near the bandits’ attack zone, and not far from it they find a big multi-family farm. They send the rogue to scout ahead and investigate, he notices that the farm doesn’t present any sign of battle, but all the windows are barricaded and there’s no one outside. He gets to the stables and sees from afar 2 people calmly tending to two horses. He can see they’re armed, but can’t make out their equipment exactly. He returns to the party, which decides to approach the farm. The farm is big enough to be divided in several buildings, so they get near one of them. They knock, no answer. They then get to another one and see there is smoke coming out of the chimney and a little noise inside. They knock and the noise stops (the people inside are slowly and silently getting ready for a possible battle, alerted by the knocking). They then get to the stables, but this time not stealthily, and the 2 people inside the stables get out while drawing their weapons. A short dialogue commences, and the 2 people order the party to drop their food (revealing themselves as bandits). The party lies saying they don’t have any, then the bandits order them to then drop their weapons and armor. The party tries to lie again to get the bandits to think there’s an entire army unit nearby, but the far-fetched lie does not work. The party warrior then insults the bandits, and one of the bandits calls for reinforcements from the nearby building (the smoking chimney one). Battle commences when the same warrior from before charges the bandit. The party takes their turn, and the first 2 bandits "waste their first action" telling the party to surrender while 8 more get there in 2 turns. The party refuses to surrender until only one of them is on his feet.

Now, the party knew the bandits were not far from where they were, had the chance to notice that something was wrong in the farm, that there were armed people inside, that those same people were too relaxed considering there were undead and bandits roaming around the zone, that the first people (the ones in the smoking chimney building) didn’t interact peacefully (or at all), they were also given 3 chances to surrender without a battle. Is it clear or not that the PCs should not have tried to fight?

P.S.
The right arm of the bandit leader even showed up for one turn, but said to the bandits "You can do this on your own, you don’t need my help" and left immediately after.

P.P.S.
The general course of action predicted was that the party should have gotten to the farm later, first talking to the city’s authorities to set up the trade route and then cleaning it up, when they would have had more equipment, experience, and maybe allies. They could have even tried to talk to the bandit leader instead of fighting, but insulting the lackeys is not a diplomatic choice.