Подумал он с странною улыбкой
which translates to “He thought with a strange smile”. I fed this English sentence back into Google Translate and got
Он думал со странной улыбкой
Is it possible that this is an example of spelling rules changing in the last 150 years?
The Instrumental case has two forms, the "normal" one and the "bookish" one. The first one is used in everyday speech and it is modern. In this case, the feminine adjective ends in -ой or -ей and the noun also ends in -ой or -ей. The second case also exists, but it is used in literature. In this case, the adjective ends in -ою or -ею and the noun also ends in -ою or -ею. Sometimes you can find the combination of both cases, as in your example.
Everyday speech, modern literature: Он был там с красивой девушкой.
Old literature: Он был там с красивою девушкою.
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