I have absolutely zero insight but if the PL rules were on genuinely shaky legal ground, I feel that Newcastle would have challenged them when they came in 3 years ago. These rules were very clearly brought in to stop Newcastle, the meeting to vote on them was called almost the same day the takeover got approved.
Reading through, it doesn't sound all that convincing to the layman.
It's worth remembeing City didn't vote in favour of the rules at the time though and the papers said this was because they thought it wasn't legal. So it's not a new theory at the club.
Other than that it's interesting that it's come from Lowton not Ziegler as the latter has had all big scoops for City v PL lately. And the reporter has clearly seen the actual documents and quoted from them.