Translation:On Wednesday, I saw Grandma's former student Matěj.
They have a similar meaning. The distinction between perfective and imperfective is little bit smaller in the past tense, at least for some verbs. With uviděl you are stressing that you managed to spot her or that you just saw her for a short moment. Then of course after this uviděl maybe you contacted her and had a discussion... that is not excluded. But uvidět is really to spot someone or something.
I will add it here as a possible translation but it is certainly not necessary.