I think vs. I'm thinking

Hi, can you please tell me why in the following paragraph the sentence reads “I’m thinking” and not “I think”? Many thanks, Torsten

Customer: Well, yes! But I’d like to start with low-cuts. I need something to complement
this outfit.

Shop assistent: I see. OK, you’re grey and black. Hmm, I’m thinking I have just the thing for you! Please wait here, and I’ll be right back.[YSaerTTEW443543]

TOEFL listening lectures: A lecture from a physical science class[YSaerTTEW443543]

Hmm, I suppose “I’m thinking” sounds a bit more immediate, or vivid, or something like that.

Although “I’m thinking…” is valid in traditional English in the right context, the use of continuous tenses for verbs such as “think”, “like”, “love”, “believe” and so on has been an increasing fad/trend in recent years, so it seems to me. In the UK it may be viewed as an Americanism.