It can be surprising because usually, you see the more common construct with an adjective and a noun both plural, and it can be counter-intuitive (or ‘uncomfortable’) even for native speakers.
But this is the way to go, as curieuses qualifies both une estime et une amitié and as this nominal group is plural (there are 2 elements), the adjective must be plural.

If we replace une estime et une amitié with sentiments, it sounds more familiar: Roland avait pour lui des sentiments curieux.

It is indeed both correct and weird for native speakers. It’s even weirder when an adjective qualifies two nouns from a different genre, a masculine and a feminine:

Julie porte un T-shirt et une jupe neufs.

Here the adjective "neuf" has to be at the masculine form because in grammar masculine always wins, but it sounds very weird when it comes right after the feminine noun!

So generally we will try to change the word order to Julie porte une jupe et un T-shirt neufs. to make it sound a bit better…

Many natives would make the mistake to write Julie porte un T-shirt et une jupe neuves. They considered changing the rule, but it hasn’t changed so far.

In this sentence, both "amitié" and "estime" are "curieuse". We know that precisely because "curieuses" is in the plural form.

Compare :

• Roland avait pour lui une estime et une amitié curieuses.
• Roland avait pour lui une estime et une amitié curieuse.
• Roland avait pour lui une amitié et une estime curieuse.

Here, we understand than only one of the term is "curieux".

Note that the last two sentences are formally correct, but not natural. They should be rewritten :

• Roland avait de l’estime pour lui, et une curieuse amitié.
• Roland éprouvait de l’amitié pour lui, et une curieuse estime.

The original sentence is quite elegant.