Q:

Proper conjugation of "to be" in this example

Is the conjugation correct here?
I know "A family were there." can be grammatical when "A family" is being treated as a plural noun. 
But the following example is different. The subject is plural but it's treated as singular.
I've never encountered this pattern before.

It is no accident that Seamus Heaney’s selected poems is titled “Opened Ground,” since writing poems for this most remarkable farm boy was a kind of digging: “Between my finger and my thumb / The squat pen rests; snug as a gun.”

So what's going on here?

A:

It's probably because the reference is to the collection of poems, and hence singular.

A:

No,this is not ungrammatical as while using collective nouns we always use "is" in the sentence. 
Below mentioned examples may make this clear to you : 
1) A hive of bees is approaching towards east.
2) A panel of experts is sitting to judge the performance
3) A team of laborers was found working there. 
So, while using collective nouns in the sentence we use singular verbs such as 'is' 'was'.
Here, in this sentence there's an indirect use of collective noun in the sentence due to which 'is' used. 
The sentence here refers to collection of poems instead of a word poems (plural form of poem)
Also, in the question "A family were there" is grammatically wrong.It should be "A family was there" as family refers to a group of people living together which is again a "Collective Noun". 
Hope this helps!!!

