Obviously, this means that the file was edited by Adobe Photoshop at some point in time, or, in the case of the Instagram app, the application adheres to a data standard previously introduced by Photoshop.

According to the developer information at exiv2.org, Photoshop stores some additional information in JPEG:

Adobe Photoshop uses the APP13 segment for storing non-graphic information, such as layers, paths, IPTC data and more. The content of an APP13 segment is formed by APP1 marker (0xFFE1), an identifier string (usually "Photoshop 3.0\000", but also 'Adobe_Photoshop2.5:', used by earlier versions) followed by a sequence of resource data blocks. In general, a resource block contains only a few bytes, but there is the important IPTC block can be quite large. The IPTC block may not fit into one APP13 segment, so it can be split into multiple APP13 segments.

The reference document for the Photoshop file format is available at http://www.adobe.com/devnet-apps/photoshop/fileformatashtml/

The linked Adobe page lists various image parameters that can be saved in the block, such as caption, border information, background color, print settings, halftoning information, etc.

The block starts with '8BIM' signature, which indeed, can be found in your text editor, in the second line, just after "3.0" (part of "Photoshop 3.0" identifier - which must be used even if the application writing the data is not Adobe Photoshop, otherwise the data block could not be properly analyzed by other applications looking for this data).