There is a lot of space on the Register dedicated to the ineptitude of British politicians when it comes to IT so to expect a system that is anything more than basic is probably a bit of a stretch. The MPs will have to set this up at home - no IT to come and do it for them so Zoom is probably not an unreasonable choice.
It obviously matters if someone zoombombs but otherwise the link does not have to be particularly secure as this is open parliament. It is more worrying that they were using it for cabinet meetings but, hey, if it provides some transparency in government... ;)