There are many things which affect our BG: food, alcohol, exercise, stress, illness, drugs, time of day, month year, weather, ...
If you are away, it is likely your usual regime has changed. Even though you ate your usual meal, you may have done more exercise or had a glass of wine which you don't usually drink, or slept in a warmer room than usual or ...
With so many things which can affect our BG, it is often not possible to work out what caused one oddity.
I keep an eye on trends and make adjustments based on these rather than one off events.
I am a little confused by one part of your message - you mention a BG of 2.5 which you treated with fruit juice and chocolate. Then you were surprised by a BG of 5.5. I do not know what is your usual fasting BG but 5.5 seems reasonable and would match with a treated hypo.