In Australia, the bases are either on the outskirts of the city or in the country areas. I imagine US and British bases and other military assets are stored away from the city (for space and real estate reasons I suppose). Thus it may seem odd for a American or British person to see a bomb hit a residential district.
I no way do I agree with or condone the bombing of civilian areas, but if the bases in Kabul are like some of the bases in Italy, if the bomb missed by 20 metres then a market place or apartment would be hit with many lives guaranteed to be lost. Even hitting the base could cause "collateral" damage.
I dont know why anyone would have military assets in a built up area, but it could be a "village walls mentality".
The "apology" by the Defence Dept is very 'weak' and serves more to inflame further anti-US sentiment.