YANBU OP. But I can't believe no one is asking what we all really want to know though - what did you buy from IKEA?
This could be an "IKEA x Found Shopping List" type thread!
I once had to leave my wheelchair outside a toilet (btw, you really can't fit a wheelchair in every disabled toilet cubicle, particularly small/independent places. I'm lucky enough that I can use a stick out of the chair) I came out to a group of boys about 13/14 riding it around 100mph and trying to do wheelies! I'm normally the type who would totally lose my shit, but they actually looked to be having so much fun and enjoying themselves so much, it actually made me smile. I did pretend to lose my shit initially and terrified them. I pointed out if they kept that up, they'd end up in a fucking wheelchair themselves in A and E, god they were mortified to be caught. They were really apologetic and embarrassed especially when I'd finished with them. I said I didn't mind myself on this occasion but that they absolutely can not go around nicking peoples wheelchairs for their entertainment, it's disrespectful/TWOC etc, as well as a dick move in general. It all ended well and I'm sure they wouldn't have done it again.
It's different from OP's situation where this adult was a disrespectful adult thief, it's indefensible (to anyone who isn't ableist or lacking any common sense at least). These were young and thoughtless. They reminded me a bit of me and my mates being dicks riding supermarket trollies in the carpark (when supermarkets used to be closed on a Sundays!) And my own DC used to love spinning around/wheelies in my chair etc at that age. Even now, my DH will do terrify me doing exaggerated wheelies pushing me up a pavement! I have to visit a usually deserted part of a certain hospital every so often, and if a DC is pushing me and there's no one about, they will run along a long corridor pushing me as fast as they can, I don't know who enjoys it more, me or them. Part is a slope and I know it'll end in tears one day, but at least it's near A and E 
Anyway, OP what did you buy? (Also I don't know how you feel about chairs and whether you can self propel or would like someone to propel you etc, but IKEA provide both types of wheelchairs, and a personal shopper/assistant on request). Shopping there in a chair, for me, is much more enjoyable than with a stick/crutches. I can take my time and look at it all instead of struggling in pain and trying to make it as short as possible. I love looking at the tiny studio flat layouts and how they fit things in. I just love IKEA basically 