Of course if he were able to use his Eye of the Ruth, this replica would not even last a second in front of his eyes. But, it is in bad taste of trying to make excuses.
He did not sense anyone here. It seems that his teacher might not appears as obvious.
There might be hints in the form of another
Dreams rarely make sense.
Loki understood that sometimes in dreams imagery is impotent. It is full of symbolism and depends on one interpretation. Loki understood why his teacher wanted to meet him in dreams.
As the Gardener, he might unable to give direct help to Loki. And as such, he could only use this kind of methods.
But this did not mean Loki trust his teacher explicitly. There is a reason why his teacher is called the God of Mischief.
Whether his teacher really wanted to help him is still something that needs to be pondered upon.
