Colin McLarty's answer clearly explained 馍夹肉 is just the Chinese writing direction ('right-to-left' instead of 'left -to- right' like English should) of 肉夹馍 , which is the correct name of this food item.
In '馍夹肉' the main noun is '肉' and '馍夹' is the adjectival phrase.
- '馍夹肉' = 'flatbread sandwiched meat'(meat that is sandwiched by bread) which is misleading description of this food item.
The main noun '肉' here is in the same role as 'the sausage' in a hotdog or 'the meat patty' in a hamburger. It doesn't describe the item accurately (a sausage without the bun is not a hotdog.)
In '肉夹馍' the main noun is '夹馍' and '肉' is the adjectival noun.
- '肉夹馍' = ' meat sandwich bread', which is the accurate description of this food item--
'肉夹馍' is a [肉(meat pile)] in [夹馍(sandwich bread)]' or simply: 'meat sandwich' (Northern China style)
Think of 'beef sandwich' (beef in sandwich bread).
From the edited question:
The shop 二丫头馍夹肉 is listed at DianPing, along with reviews writing e.g. "店里馍夹肉真不错" and "馍夹肉的馍不错".
There are many examples of huge mistakes in stores signs.
Examples of mistakes found in actual store signs:
1.錯別字:梁瓜 正字:涼 出處:大成街市熟食中心
2.錯別字:石班 正字:斑 出處:新都城新雅海鮮酒家
3.錯別字:豬利 正字:脷 出處: 寶林紫荊大酒樓
4.錯別字:栗米 正字:粟 出處:厚德萬有街市
5.錯別字:雞亦 正字:翼 出處:厚德萬有街市(佳寶)
6.錯別字:朱扖 正字:豬 出處:綠河茶餐廳
7.錯別字:麵飽 正字:麵包 出處:麵包先生(麵包鋪)
8.錯別字:支竹 正字:枝 出處:喂食貓茶餐廳外賣單張
9.錯別字:九菜花 正字:韭 出處:喂食貓茶餐廳外賣單張
10.錯別字:痛証 正字:症 出處:元朗宏發徑生生保健中心.
11.錯別字:人仕 正字:士 出處:天水圍聖腓力教堂佈道會
12.錯別字:禮卷 正字:券 出處:衛訊PhoneShow 9月p.21
13.錯別字:拼盆 正字:盤 出處:元朗明星海鮮酒家.
May be the owner of 二丫头馍夹肉 saw a sign 馍夹肉 somewhere like you did and mistaken it was the correct term and put it in their store sign....
Also, The reviewer saw 馍夹肉 in the store sign, trusted the owner and called the 'meat sandwich bread' 馍夹肉 as well.
Finally: look at 牛肉夹馍; 羊肉夹馍, 孜然羊肉夹馍. That should clear up the confusion.