It could be harmless. What we have to remember is the somewhat narrow focus some people living in apartments have. This is particular in the elderly/disabled complexes. These people mostly live in their "box" and their minds are focused on what they can see from it and around it. Most of us property managers realize things of this nature could get dangerous, but we still like to opt for a conventional approach.
When I managed an elderly/disabled, I could hardly walk the property without some of the tenants wanting me to come in and have coffee and just talk, or I would look up from the desk and here would be a little old lady with a tin foil wrap of cookies she has made me. The artist could be in the same situation, where maybe is impressed with you, and wanted to try and get your attention. As we all know, the cardinal rules of managing tenants are the three "F's"---Fair, Friendly, and Firm.
I would take the drawing with a tone of ease, but I would keep that little mental note on it. If nothing else happens pretty soon, it is probably all ok.
To add a funny note to this, we had one apartment with a window in the North, West, and South side. It was "Observation Central" for the entire complex. The little old lady could observe everything everyone did and she knew if a fly lighted on any part of the complex, except the East side. I noticed the mini blinds on these windows were constantly being bent up. After replacing them the second time, I showed the lady how to tilt the blinds upwards, so she could "watch outside" and no one could see her standing at the window. I then took her outside to prove she would be hidden while observing out the windows. I never had to replace the blinds again!!!
I could also get reports from her (briefings actually) on everything that happened while I was gone, if I wanted them. LOL