A little firm, maybe. But huge German firm Flixbus?! For a nation which applies rules & regulations so strictly, they deserve banning here.
I think you need to understand what Flix actually is. It isn't a major transport company with consistent standards like e.g. National Express, it's more of a transport exchange where small to medium coach companies of decidedly mixed repute partner with them on a revenue sharing basis (with the coach company if I recall taking most of the revenue risk). That's how it has expanded so quickly. It could be compared perhaps to the fast expansion of the Subway sandwich chain which is I believe 100% franchised and as a result you get extremely variable quality of service.
National Express of course does a lot of subcontracting, but has a much tighter control on it and does operate some coaches itself.
There are plenty of UK coach companies of lesser repute where I'd expect exactly that kind of unacceptable response, though I don't know if they contract for Flix or not. It's unlikely the member of staff who showed up actually worked for Flix, more likely they worked for the coach company.
Because coaching is, by and large, about the lowest price being the only thing that matters (because if you could afford it why wouldn't you fly or go by train instead?), this approach does extremely well in the market, and makes things hard for companies like NatEx with a view more towards quality both in terms of the soft and hard product but necessarily at higher prices.