Who using Pretérito in the first sentence and Imperfecto in the secend? Both are said to be non-permanent conditions.

Hola Per Ivar,

If you are referring to the sentences in the lesson, the first one is using the present tense "¡Vaya! Mis gafas están rotas." and the second one is using the imperfect tense "Sus pantalones estaban sucios."; but it doesn't matter which tense you use with estar in this case. This lesson is about using "estar" (not the other verb meaning "to be", ser) to talk about a physical condition. You can use different tenses.

I hope this clarified it.

Saludos

Inma