The referee is most likely talking to the defensive line, instructing them to hold before the ball is brought back into play with the foot.

Spot on.

The days of Robin Whitfield and the like blowing for a penalty just so they could have a rest are well behind us, thankfully.

The real problem is inconsistency, if a ref wants to let the game flow then play that way all the way through for both sides, if they are going to be pedantic then play that way all the way through for both sides. But I want to see them consistent week in week out, as changing their interpretation from game to game leads to the suspicion that they are being influenced by the playing styles of different sides. Anyone with half a brain knows all sides want quick ptb in possession and slow ptb when defending, but most sides are better at one than the other, or focus more on one than the other, so the interpretation matters not just within in a game, but from week to week. If a ref decides to hammer slowing tactics one week and then is more lenient with same tactics the following week it looks like he's showing bias between teams.

Not playing the ball with the foot is something that needs to be clamped down on as it happens numerous times in every game. I can recall a team going an entire set of six without playing the ball correctly once during a game this year.

If I remember correctly, the player only needs to attempt to make a play at the ball rather than actually using his foot.