It's true that they didn't impersonate letsencrypt, but they did:

1. Assign DNS records to these two domains and remove them after someone exposed these domains. https://groups.google.com/d/msg/mozilla.dev.security.policy/...; https://archive.fo/MQwMK; https://archive.fo/0HQZ7

2. Send marketing e-mails that exaggerate threats of using a "foreign CA", such as Let's Encrypt: https://groups.google.com/d/msg/mozilla.dev.security.policy/... (Well, "Percy" has always been bringing it up.)

While (2) has been something too old to keep bringing up, (1) certainly undermines some of Richard Wang's claim.