I"m honestly surprised that someone would be offended by this. Clearly they misunderstood something your colleague told them. She's a local to Thailand, you said - was she not effectively able to communicate about the second reservation?

I think it's great that the front desk called to ask your permission and didn't just give out your room number to anyone who asked. I guess your colleague might be offended that they thought she was a prostitute, but I'm sure there are all types.