Food lesson 8 claims to teach the word raději, but I just redid it and it did not include that word at all...
It came up a little for me, but not in the context of "prefers." The translations kept coming up "likes" for the use of "have"+this word, but when I said "Matej likes tea" just now it was marked wrong because he <prefers> tea.
Raději is the comparative of rad, similar to radši
If you "mám rad", then you like something; if you "mám radši/raději", you like something more than other things, in other words; you prefer it.
(And if you like something the most, you add the superlative prefix "nej-" in addition to the comparative suffix "-ěji" -> nejraději.
You were probably seeing rad or rada. Matěj má rad čaj would translate to "Matej likes tea", but in the situation here it's being consistently translated as prefers throughout the course.