Is it rude to refer to janitors as 'floor people'?
Solution 1:
This may be subtle and comes down to inflection and intention. I suspect that your manager was not being rude but trying to refer succinctly to a particular trade.
If you were talking about a construction site you might talk about the "concrete people" or the "drywall people" to refer to the particular trades that were expert in those parts of the project. Those trades may have more precise professional nomenclature to them, but to an outsider it may be a useful shorthand that identifies the work without knowing the terminology. If your manager was talking about waxing the floor-- which is a skilled task that may also imply something beyond a regular custodial service-- then presumably he was using "floor people" as a shorthand for that skill.
You could, of course, also intend this phrase to be a form of deliberate (and surprisingly poetic!) put-down pun by using the physically "low" location of a floor as a metaphor for class or status. I don't know you or your manager but most people aren't jerks by default.
Solution 2:
It depends on the implication. If you assume "floor" to be a metaphor for "the lowest strata" or "beneath my feet" then certainly, it's derogatory.
However, I don't think this was your manager's intention. Instead, in his question, "floor people" is an ellipsis of
the people whose job it is to clean the floor
This use is much the same as saying "the printer guy" or "the cleaning lady", and so it's not meant as derogatory. Nevertheless it is somewhat insensitive, in that it can be easily misinterpreted.
Note that it can be rude also to talk about people by their function rather than their job title, but again this is highly context-dependent. For example it would be familiar, but not derogatory, to say something like
You should go see Dr. Wallace, he's the top heart man in the country.
Solution 3:
I agree with the other answers that your manager meant "the floor people" as a neutral way to refer to the people whose specific task was to clean the floor as requested. I want to add something to that:
he had put in a request last week for our janitors to mop up and then re-wax the tile floor in our area this morning.
It's important to your manager that this floor gets cleaned and re-waxed soon. By saying "the floor people" instead of "the janitors" he's indicating that he wants to know specifically whether you saw anyone working on the floor.
Also, re-waxing a floor is a specialized job that your usual janitors might not have the equipment and training for; so he might have been wondering whether you saw different people than usual.
Solution 4:
I think it should be made clear that in English usage floor person is never used in any sense other than 'person with some function connected with a floor'. There is no connotation of lowly status, (and no connotation of high class in ceiling person). It's just a factual description.