I think the framing was ignorant & tbh it's why Twitter is such a terrible place for discussion in general but particularly on complex subjects. There's some truth in what he's said but he's expressed it in a way that's offensive.
I worked on a project a few years ago mapping crime in certain areas in Manchester & the pattern on street crime is v similar across the UK especially in large cities. There are people who beg who are in dire straights, often with mental health problem and/or addiction issues etc. and that's one of the areas this boxer says he's got concerns on, having grown up & lives/lived in a deprived area in Edinburgh. And there were also people arrested for begging who weren't homeless, but were picked up/dropped off in cars from outside the area (those without an address were referred onto support services as an alternative to conviction with any prison time etc.) and who had homes but chose to do this instead of work etc. It is a problem with some people who are 'on the street' who beg but have no need & aren't actually homeless or have any addiction issues (they were often drug dealers as well, pushing drugs onto others on the street who were vulnerable & were addicted). But they weren't limited to 1 particular demographic & that's where the ignorance comes into what he's said.
He might well have witnessed illegal/fake begging scams, or he might have witnessed people who were trafficked & coerced by criminals etc. It's the limiting it to a single demographic when he's really not got the knowledge to know that's the case that's the issue.
But it's why Twitter for this stuff is terrible & at the very least someone should have been on top of this to ensure, if he's not stupid & is a 'decent guy' as many I've seen on Twitter say he is, his social media should have been cleaned up before he was announced. If they'd been planning this for months, that should have been high up the list of things to cover.
It's piss poor vetting/due diligence. And for a party that wants to be taken seriously, it's a terrible look for both the candidate & the party.