why does '-e' work differently in guix shell and guix package?

[Alexander Asteroth]

When I do
```
$ guix shell --network --container --emulate-fhs bash coreutils -e 
'(list (@@ (gnu packages commencement) gcc) "lib")'
```
I get a shell, that has `libstdc++.so.6` in `/lib`.

But when I do
```
$ guix package -e '(list (@@ (gnu packages commencement) gcc) 
"lib")'
guix package: error: expression "(list (@@ (gnu packages 
commencement) gcc) \"lib\")" does not evaluate to a package
```
I get an error. Why is that?

Cheers
Alex

PS: reason I'm trying that is, that the recent pytorch-version 
installed via pip complains about not finding libstdc++ which is 
in the lib output of the superseeded gcc package and I thought 
this might resolve my problem.