Straight from the article:

Researchers also found that 12.3 per cent of cannabis users with pre-existing anxiety but no record of hospitalization visited an emergency room or were admitted to hospital because their anxiety symptoms worsened. … While some people may self-medicate by using cannabis to relieve anxiety, there is no robust evidence to suggest it is effective for that purpose, Myran said.

Weed is already known to increase anxiety for some people. It’s not just discovering that they had a prior anxiety issue. This is clearly making an associating with weed and increased overall anxiety. Albeit just a correlation until it can be proven.

Anecdotally it has been something I experienced until I lightened up on edibles.