It's kind of more a pattern of that - Tory activists/campaigners being shipped around constituencies and the hotel bills for putting them up not being declared in amny of the constituencies they were working in, but against a central Conservative party account. So it looks much more like wilfully breaking/evading the rules on election spending than an administrative oversight because they did it several times i.e. it looks rather like overt electoral fraud.
It's technical rule breaking - they weren't stuffing ballot boxes or anything - but breaking the rules is breaking the rules, which it rather looks they did intentionally.
This has serious consequences as, theoretically, the conservative candidate in each constituency they worked in could be removed from their office and by-elections called in all the constituencies in question. When the government has a majority of 12, that can soon matter - bear in mind if a conservative member gets ousted by a labour candidate in a by-election, that actually depletes the majority by two, so you only need it to happen a few times and the government is in serious hot water. And they won't have bothered shipping in campaigners to safe seats an yway, so all of these must be fairly marginal..
