Maybe some are only using the telegram bot for only mentions and tracked boards or topics, some may not really put mind on the ignore function as well that is on the bot, moreover, many users don't even mind putting people on their ignore list except on severe cases, so don't expect much attention on the use of ignore button.
Once you ignore on forum you probs won't see their post even if you saw a mention on the notifier.
Depends on what made you ignore such person, if it's about spam then you obviously don't need to even see when they quote you in a thread or mention you.
if it's something else that doesn't really concern not reading their post when they mention you or quote you then you can still let it be on the notifier, it will be left to you to read or ignore tha particular post. I can ignore someone because I find his post annoying but still concerned about what they are trying to pass to me.