The pop-up hints are indeed not very useful.
«Соба́ки» can be either nominative plural, or genitive singular. Since you use genitive after «нет», in this sentence, «соба́ки» can only mean 'dog' ('dogs' would be «соба́к»). However, the hints don't take this into account.
I believe the hints are generated automatically and the course maintainers can't do much to them. So just try not to rely on them too much.