Sequence
In the previous verses (70-72), breach of faith committed by the people of the Book was mentioned. This included disbelieving in the verses of Allah, confusing the truth with what is false, concealing the truth and conspiring to mislead Muslim believers.
In the verse cited above (75), their breach of trust in matters of property has been mentioned. Since some of them happened to be trustworthy, both types were identified.
Commentary
Praising good qualities in some non-Muslim is correct
In this verse (75), some people have been praised for their trustworthiness. If this 'some' refers to those among the people of the Book who had embraced Islam, praising them poses no problems. But, in case, it does not refer to Muslims particularly and instead, refers to the people of the Book in the absolute sense including non-Muslims as well, then the situation generates the question: When no act of a kafir (disbeliever) is acceptable why praise them?
The answer is that for an action or deed to become acceptable is a different matter and having a word of praise for it is something else. From praising something it does not follow that it is acceptable with Allah. The purpose is to point out that something good, even if it be that of a kafir (disbeliever), is good enough in a certain degree, the benefit of which he receives in the form of good reputation in the mortal world, and of course, in the Hereafter, in the form of a reduction in punishment for his disbelief.
This statement also makes it, clear that Islam does not resort to prejudice and short-sightedness. On the contrary, it shows open-hearted appreciation of the excellence of even its adversary in respect
of his achievements.
It is from this verse: إِلَّا مَا دُمْتَ عَلَيْهِ قَائِمًا (unless you keep standing over him - 75) that Imam Abu Hanifah (رح) has deduced the ruling that the lender has the right to keep pursuing the borrower until he receives his due. (Qurtubi)