Hospitality is a fundamental virtue. Skimping out on food is maybe the fundamental transgression of norms. The anger is subconscious and maybe primal.
I was a "contractor" from an in practice body shop consult agency, not an actual contractor. I did every day office work for three years, being part of a normal work group going to every day meetings etc.
But I don't think that matters. If you have an actual consultant in the office, being there once a month, you give him strawberries too, if you hand out strawberries.
Also, the pay was somewhat lower. I was fresh out of uni so I didn't know better.
Notably, only bosses two layers up thought it was a good idea to skimp on the strawberries etc. The bosses that had to deal with the ensuing bad mood ensured there was no such distinction between FTEs and "contractors".