Unless your tv has dual tuners, which most don’t because $, or use an internet connection to populate the TV guide, that’s how digital TV guides work.
Some TVs will sweep through the channels populating the EPG while the TV is ‘off’ or store EPG data it received earlier, so as long as it’s been plugged in recently it’ll have a reasonably up to date EPG data right away.
Some TVs will sweep through the channels populating the EPG while the TV is ‘off’ or store EPG data it received earlier, so as long as it’s been plugged in recently it’ll have a reasonably up to date EPG data right away.