My own definition does not matter. Swiss law matters:
'The order may require real-time surveillance to be carried out and the handover of the retained secondary data of telecommunications from past communications (retroactive surveillance).'
The question is not whether ProtonMail has access to user data. (They have, you are absolutely right.) They question is if they perform real-time surveillance, i.e., lawful surveillance (whether voluntarily or not).
No matter what they actually do, they'd be idiots to reply to this, which is why we won't see a reply from them. Doesn't really say anything meaningful.
You're asking a loaded question. Of course they have access to some real-time data re users.