Did they also testify under oath there is no lawful intercept API or anything similar? That does not require logs. In fact when the feds would set up phone call intercepts on telco switches we would intentionally disable logs and put the mainframes into "test mode". And that is even before people start playing legal word games like calling lawful intercept "debugging" or something else. Lavabit [1] found out what happens if lawful intercept is not available.
Just me personally, I would always assume a service I do not entirely control and operate is doing what it can to comply with lawful intercept requirements and they are likely playing word games to not drive away their members and I would not blame them. I am just the properly paranoid type in part due to a good upbringing by a properly paranoid person.