Holy Thursday is not a holy day of obligation. You are perfectly free to not attend that day. The same goes for Good Friday.
Perhaps someone has gotten confused with Ascension Thursday. That is 40 days after Easter and is a HDO, but it is often transferred to the nearby Sunday, so ends up not really being an extra day that you have to go.
The HDO can vary by your locale, so you may need a local answer. Where I live they are:
and the Ascension.
Some years about half of them get transferred away to the nearest Sunday or abrogated somehow, so it can be hard to keep track.