It could be either, and both may contribute. Several photographers noted that fingerprints, oil, or other smudges on the front element can light up strongly when shooting toward the sun, producing a hazy or streaky flare. Others pointed out that the example also looks like ordinary veiling flare from strong backlight, possibly with sensor-related diffraction effects.

So the safest conclusion is: this is not necessarily “just” lens flare. A dirty front element can make normal flare much worse.

To reduce it:

• Clean the front element carefully.
• Use a lens hood to block stray light.
• Shade the lens with your hand or change your angle slightly.
• Keep strong light sources just outside the frame when possible.

A clue: if the effect appears mainly when shooting into bright light and changes a lot with tiny shifts in angle, that suggests flare; if it looks unusually smeared or hazy, check for fingerprints or smudges first.