As far as i know the expression “a glimpse of nibbana” does not occur in the Pali texts and it’s meaning is open to interpretation.
Nibbana as word is in the texts used in a great variety of context and takes on a variety of meaning.
As an example Nibbana in definitive and in a qualified sense;
Extinguishment Is Visible in This Very Life
“Reverend, they say that ‘extinguishment is visible in this very life’. In what way did the Buddha say extinguishment is visible in this very life?” “First, take a mendicant who, quite secluded from sensual pleasures … enters and remains in the first absorption. To this extent the Buddha said that extinguishment is visible in this very life in a qualified sense. … Furthermore, take a mendicant who, going totally beyond the dimension of neither perception nor non-perception, enters and remains in the cessation of perception and feeling. And, having seen with wisdom, their defilements come to an end. To this extent the Buddha said that extinguishment is visible in this very life in a definitive sense.” SuttaCentral
Furthermore Nibbana can be explained as destruction of Taints;
“Venerable sir, it is said, ‘the removal of lust, the removal of hatred, the removal of delusion.’ Of what now, venerable sir, is this the designation?”
“This, bhikkhu, is a designation for the element of Nibbāna: the removal of lust, the removal of hatred, the removal of delusion. The destruction of the taints is spoken of in that way.” SuttaCentral
These are just a couple examples and furthermore there is the distinguishment between Nibbanadhatu with and without a residue fuel but i won’t get into that here.
Therefore it is hard to tell what people mean by “A glimpse of Nibbana” because in a sense even a worldling can realize first Jhana and experience a glimpse of Nibbana in a qualified sense and here any sense of release is qualified to be called release.
Talking about Nibbana in a definitive sense refers to the unsurpassed release without a sequel, final freedom which can not be surpassed.
I would say Stream Enterer experiences Nibbana in the sense that he discerns the unconditioned state void of delusion which is the unsurpassed release and therefore it is Nibbana in definitive sense but “the glimpse” can be explained in various ways ie his incomplete removal of fetters but removal nonetheless or a glimpse in sense of having discerned the cessation of the unconditioned he discerns the arising of the conditioned after emerging from the attainment.
I think it is a very vague term and needs quite a lot of clarification and if one was to stick to the Sutta definitions it is a stretch to call insight into non-self a glimpse of Nibbana because even in the qualified sense the Sutta restrict the use of the term and mere understanding or realization of non-self seems to be beyond the scope provided by the Sutta.
Either way the expression can take on various meanings so one can make pretty much anything work with clarification but some expressions are going to be misunderstood more than others.
I am pretty sure i know some people who basically managed to quit smoking and think they have attained at least a glimpse of Nibbana on account of that or something like that. I personally try to be a bit more orthodox in the way i express myself to avoid confusion.