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You're allowed to ride together, just not drafting.
I rode side by side with a few people and chatted. However, I think it is against the rules and would have been much more cautious about doing it if I'd been anywhere near the front of the race.
The manual deliberately doesn't define drafting but says refer to your local TT rules. And as CTT says drop back if passed, side by side wouldn't be allowed.
I doubt they'll get disqualified or even penalised but they will surely ride together to Cannakale now!