- Is it true or superstitious?
Calling those things apshagun has no connection with superstitions nor they are just 'religious' things. In previous days, we had no sources of power like we have today. People used to depend on sunlight in day and candle or 'diya' in night. So diya bujhna i.e. Fire going off used to be really bad thing as they end up in darkness. that's why it is considered as 'not good' (Apshagun i.e. Which does not bring Shagun) thing, but unfortunately even in this era we carried that education as it is without even thinking cause behind it.
Similar thing you can say about breaking of glass. We have plain marble floors today at our home. But in previous time (few centuries, not too much previous as glass was not even invented that early), they didn't have such cleanable floors. So breaking glass on that rough muddy floor and then picking all the tiny pieces up without vacuum cleaner can be really tiring (plus no guarantee of cleaning it 100%). That's why it is also considered as 'not good thing' again. There is no such thing as apshagun as our Hindu religion heavily based on science and causes not just religious beliefs.
- Is there any reference from scripture?
Well I don't exactly know the answer of that question as there is not just one holy book in Hindu religion and I have not read all of them. But I can tell you this definitely that There will not be anything in any holy book telling about superstitions without giving the "cause" behind it. you just have to think about it and research if possible.